Generally, a fluorescent lamp and an incandescent lamp have widely used as a light device. The incandescent lamp has low efficiency and economic feasibility due to high power consumption, and thus demand of the incandescent lamp has recently reduced.
A light pipe, which is an element that transmits light from a light source through the inside of the light pipe, has gained much interest in recent times because of its ability to transmit light to remote locations with relatively little transmission loss and its potential for allowing small thicknesses in products.
In the related art, a light pipe includes an air layer, with a diffusion surface or a reflection surface having prism patterns, on the inside or outside of the light pipe. The light pipe outputs a light inputted through the air layer by using the diffusion surface to outside, or delivers the light by using internal reflection through the reflection surface.
Here, it would be desirable if the light that is outputted from a light source and inputted to the light pipe could be transferred to the output end (far end) of the light pipe uniformly, but due to the hot spot phenomenon that occurs at the input end of the light pipe, the light may not be transferred uniformly over the entirety of the light pipe. The hot spot phenomenon occurs at a diffusion layer formed for outputting uniformly the light, and uniformity and brightness of the light at middle or the output end of the light pipe may be lowered due to the hot spot phenomenon by the diffusion layer of an input end of the light pipe. To solve this problem, several LEDs are installed inside the light pipe to increase uniformity in a diffuser type light pipe, but power consumption and manufacture cost become higher because the number of the used LEDs increases and it is difficult to realize the light device with thin size.